1. Field of the Invention
This invention relates to fine feed systems, and more particularly to a fine feed system suitable for finely feeding a movable portion of a measuring instrument or the like.
2. Description of the Prior Art
With general measuring instruments such as a coordinate measuring instrument and a projector, in order to improve the measuring efficiency as a whole, it is necessary to finely feed a touch signal probe holding member, a table having rested thereon a work to be measured and the like for example as occasion demands. For this, there are many cases where a fine feed system is switchable to and from a rough feed system.
Of the fine feed systems described, there are known the inventions disclosed in Japanese Utility Model Kokoku (Post-Exam. Publn) No. 33439/82, Japanese Utility Model Kokai (Laid-Open) No. 32412/83 and the like for example, which are mainly intended for the convenience in switching and obviating the backlashes. The invention disclosed in Utility Model Kokoku (Post-Exam. Publn) No. 33439/82 will hereunder be described with reference to the coordinate measuring instrument as shown in FIG. 1 attached thereto. The fine feed system is of such an arrangement that a movable member is feed by manual operation at high speed to a position directly in front of a work, a half nut is threadably coupled to a guide rod by the operation of a lever in the vicinity of the work, and, in this condition, a fine feed is performed by the operation of a control wheel. In this case, if the lever is returned after the measurement, then the threadable coupling between the half nut and the guide rod is released, so that the feed at high speed can be conducted again.
However, with the conventional system of the type described, in order to make it possible to finely feed the movable member no matter where the movable member may be, the above-described mechanism, such as the guide rod, should be provided over the whole stroke of the movable member, thereby presenting problems from the viewpoint of accuracy as well as economics. Furthermore, upon completion of the fine feed, the fine feed system should operate to be effect restoring to the original position to thereby be ready for the next measurement of the work, thus requiring the troublesome operation. Particularly, when the center-to-center dimension between a plurality of terminal holes formed in a printed circuit board and the like, if the aforesaid restoration operation is neglected, then a stroke limit occurs during the fine feed, whereby, after the fine feed is temporarily released, reengagement is needed, so that the measurement has been practically neglected from the viewpoint of the construction.